Gable top cartons have been known for the better part of the twentieth century. Their characteristic simplicity and resealability have helped to sustain their popularity as cartons for traditional liquid food products such as milk and juice, but in recent years they have been used for products ranging from ammunition to Epsom salts. Gable top cartons typically start out as generally rectangular carton blanks made of laminated paperboard or similar material. The carton blanks are provided with a number of creases to facilitate folding and forming the blank into a carton.
During decades of development, manufacturers of packaging machines have devised a variety of ways to form, fill and seal gable top cartons. Today, the most prevalent packaging machines for filling and sealing gable top cartons are adapted to receive the carton blank after it has been side sealed. The process of side sealing involves sealing opposite vertical edges of the carton blank together to form a polygonal (usually rectangular) sleeve. The sleeve is received on an indexable mandrel wheel which rotates the sleeve into respective positions where the end of the sleeve extending outwardly from the mandrel is folded and sealed to form the bottom of the carton.
After the carton bottom has been formed, it is removed from the mandrel and transported to a filling station where the carton is filled with product. Once the carton has been filled, the top of the carton is folded into the familiar gable top configuration and is heat sealed, thus completing the packaging process.
One example of a known packaging machine that operates generally in accordance with these principles is described in U.S. Pat. No. 3,789,746 to Martensson et at. Other examples of such packaging machines are described in U.S. Pat. No. 3,820,303 to Martensson et al., U.S. Pat. No. 4,759,171 to Bruveris et al., and U.S. Pat. No. 4,790,123 to Ljungstrom et al.
The use of mandrels for forming the bottoms of cartons limits the speed with which the bottom of the carton is capable of being formed, limits the maximum size of the system necessary to carry out the bottom forming process, and necessitates direct contact between the mandrel and the inside of the carton. A single mandrel is capable of forming only one bottom at a time. Increasing the speed of the bottom forming process requires introduction of multiple mandrels resulting in potentially inefficient use of space and energy. In addition to problems of space and energy efficiency, contact between the inside of the carton and the mandrel during the forming process compromises the hygiene of the container. Furthermore, introduction of the mandrel into the carton interior creates a risk of damage to the thermoplastic layer of the carton which comprises proper package formation and functionality.
Trends within the field of packaging machines point toward increasingly high capacity, hygienic machines, intended for rapid, continuous filling and sealing of a very large number of identical or similar packaging containers, e.g., containers of the type intended for liquid contents such as milk, juice, and the like. One such machine is disclosed in U.S. Ser. No. 08/190,546, filed Feb. 2, 1994, which is hereby incorporated by reference. The '546 application discloses, among other things, a mandrel-less packaging machine that utilizes a carton having a gabled bottom that is first sealed and then compressed to form a bottom on which the carton may rest. This is opposed to the mandrel-formed bottoms of prior cartons. An alternative bottom forming mechanism to the one described in the '546 application is set forth.